Thermionic discharge device



THERMIONIC DISCHARGE DEVICE April 16, 1929.

Filed Dec. 1924 WITNESSES: ii 55 INVENTPR j j M, flona/d 6 l/ff/e ATTORNEY Patented Apr. 16, 1929.

UNITED STATES PATENT OFFICE.

noNALD G. LITTLE, or WILKINSBURG, PENNSYLVANIA, ASSIGNOR To WESTINGHOUSE ELECTRIC & MANUFACTURING ooMrANY, A CORPORATION or PENNSYLVANIA.

THERMIONIC DISCQEEARGE DEVICE.

Application filed December 4, 1924. Serial No. 753,834.

My invention relates to thermionic discharge devices, and particularlyto structural features of such devices.

An object of my invention is to provide a space-current device particularly adapted for the translation of relatively large powers and for the production of short waves.

Another object of my invention is to provide a thermionic discharge device having a minimum electrostatic capacitance between the electrodes thereof.

Another object of my invention is to provide a thermionic discharge device which may be readily assembled.

Another object of my invention is to pro vide a thermionic discharge device adapted to be utilized as a satisfactory oscillation generator at extremely high frequencies.

Another object of my invention is to provide an improved thermionic discharge device adapted to be utilized in the generation of very short radio waves.

Another object of my invention is .to provide a thermionic discharge device having a grid-lead construction adeqiiate to conduct the very large grid-charging current required for generation of very short waves.

Another object of my invention is to provide a thermionic discharge device in which the capacitance of the tube structure is a part of the parallel resonant circuit of the oscillation generator.

In the prior construction of high-power thermionic discharge devices, it has been customar to provide triodes in which the material o the anode is a portion of the container, and is, therefore, adapted to be cooled by the application of cooling fluid to the outer sur* face thereof.

In combination with such a fluid-cooled anode, it is common to use a box truss-type of construction for a control electrode, and to use a plurality of looped filaments therewithin.

Types of construction which have been found suitable for medium high frequencies of oscillation, and for the generation of medium wave lengths are shown in the co-pending applications of Wallace G. Wade, Serial No. 751,508, Serial No. 751,510, and Serial No. 751,512, all filed on November 22, 1924:, and assigned to the Westinghouse Electric and Manufacturing Company; and in the copending application of I. E. Mouremtsefl',

Serial No. 5,073, filed January 27, 1925, and assigned to the Westinghouse Electric and Manufacturing Company.

In the utilization-of trlodes constructed according to the prior art, difficulty has been experienced in generating high power oscillations at frequencies corresponding to wave lengths less than 100 meters. One of the difliculties has been due to the relatively high inter-electrode capacity of the device, because the structure of the cathode, and the grid were closely related over a considerable portion of their length which was not active in the production and control of the electron stream.

' The control electrode and the filament of I such triodes haveboth been supported from the same end of the device and from the same insulating structure. This not only brings thesupporting portions of the electrodes undesirably close, but also increases the inter-' electrode capacity. It also increases the strains due to electrostatic forces impressed between the electrodes, and upon the insulating members.

Another difficulty in the use of high power trlodes operating with short waves is that a large charging current is required by the grid electrode for controlling the electron stream.

Even though the "actual capacitance in the triode be relatively small, the charging current necessaryto produce the required control potential upon the grid at higher frequencies is relatively large. When using extremely short wave lengths at their correspondlng very high frequencies, this charging current becomes so heavy that great difficulty is experienced in passing it through the customary lead wire into the triode without injuriously heating the device. 7

My invention provides a structure in which. the cathode and control electrode are supported from insulating members attached to opposite ends of a tube structure whereby maximum possible separation is obtained between the thermionicallyinactive supporting portlons of the electrodes, and whereby high conductivity to the grid electrode isobtained, with high mechanical strength.

This construction, which produces high conductivity'to the grid, also provides high mechanical strength whereby the grid is held firmly in position. This is of great importance in using short waves which would otherwise have the frequency thereof changed by movement of the grid.

Other objects and structural details of my invention will be apparent from the .tollowing description when read in connection with the accompanying drawing, wherein:

The single figure is a view, partially in longitudinal section and partiall in elevation of a structure embodying a orm of my invention.

In the drawing, an anode 1 has attached to its ends, vitreous closures 2 and 3 by means of seals 4: and 5. These seals t and 5 may be produced by the method disclosed in the application of Kirwer, Serial No. 665,55, filed Sept. 28, 1928, and assigned to the Nestinghouse Electric and Manufacturing Company.

Closure 2 has sealed thereto, a cap portion 11, to which a metallic sleeve 12 is attached as by brazing. A self-supporting box truss-type of control electrode 13 constructed as described in the previously-mentioned application of l/Vade, is positioned surrounding the filamentary cathode structure 9 and suitably attached to the mounting tube 12.

The relatively large size'of tube 12 and cap 11 provides a large section of material for the conduction of current to the grid 13,

thereby permitting the necessary currents to flow with small resistive loss. Inasmuch as skin effect becomes important at the very high frequencies at which this tube is utilized, the large surfaces of tube '12 and cap 11 provide additional advantageous conductive properties. The large diameters tube 12, cap 11 and closure 2 also ensure a very substantial mounting for the grid and the position of the grid 13 with respect to anode 1 within the necessary very small limits. 'Ihe entire grid structure with the leadin connection thus constitutes, what may be called, a high-frequency conductor, that is a hollow conducting body, which conducts current along its outer surface only, under substantial elimination of eddy currents.

Closure 3 has a reentrant portion 24, upon which is formed a press 25, through which lead wires 6 and 7 are passed. Press 25 also has therein a support wire 8. Upon leads 6 and 7 and support wire 8, there is mounted a filamentary cathode assembly 9 constructed as disclosed in the previously mentioned ap-' plications of Wade.

The anode 1 may be provided with a surrounding jacket 14, the ends of which are enclosed by end pieces 15 and 16 and which also has inlet and outlet members 17 and 18 for the admission and discharge of cooling fluid.

In the construction of my device, both ends of the anode cylinder 1 are prepared as disclosed in the application of Kirwer and the double-flap seal portions attached thereto. The cathode portion is then prepared as described in the. applications of Wade, prervoaoae viously mentioned. The closure portion 3 is then attached to the seal portion 5 in the usual way and the mount, comprising the assembly of cathode structure, the re-entrant portion 24 and the press 25, is sealed to the closure 3. In the course of this sealing operation, it is readily possible to obtain an accurate positioning of the cathode structure 9 within the anode 1 because of the ready visibility through each end of the anode cylinder.

Upon the completion of the mounting of the cathode structure, the control electrode structure may be similarly mounted, the control structure being assembled as disclosed in the applications or l/Vade. The control electrode is then attached to cylinder 12 which had previously been attached to cap 11. The cap 11 is attached to the vitreous portion 2 by the previously disclosed seals. This assembly may be called the grid mount and is, in turn, assembled to and within the anode structure 1 by the customary sealing operation. In this operation also, accurate positioning of the grid structure is readily obtained because of the visibility through both ends of the anode cylinder and its transparent vitreous closures.

By means of the construction outlined, I am enabled to produce a thermionic discharge device capable of translation of high powers and in which minimum electrostatic capacitance is obtained. It has been suggested that a minimum tube impedance is obtained because of the large area of the cathode surface and its large electron-emitting capacity and also because of the relatively close spacing between electrodes. In the device of my in vention, this close spacing is obtained and, at the same time, a maximum separation of the portions or": my devicenot directly concerned with the electron stream is also obtained. I likewise obtain high conductivity to the grid structure and high rigidity between the respective elements oi the triode.

In the operation or? triodes for the genera tion of oscillations, it is customary to use a resonant circuit comprising the inductance and a capacitance, the natural oscillation period of which determines the generation firequency. The very high conductivity of the grid electrode of my device makes it possible to utilize the capacitance between the grid and anode electrodes as the capacitance oi the resonant circuit, thereby avoiding the necessity of additional condenser means in the circuit.

By the construction as outlined, and its relatively small inter-tube capacitance, I are. enabled to so reduce the total capacitance in an oscillatory circuit in which my device is installed, as to make possible the generation of higher frequencies at higher powers than has previously been possible.

While I have shown but a single embodiment of my invention in the accompanying drawing, it is capable of various changes and modifications therefrom without departing from the spirit thereof, and it is desired, therefore, that only such limitations shall be placed thereon as are imposed by the prior art or indicated in the appended claim.

I claim as my invention:

In an electron-discharge tube comprising a plurality of electrodes and an evacuated vessel enclosing the same, a control electrode comprising a reentrant metallic tube insulatingly sealed into said vessel and constituting a portion of the walls thereof, a plurality of standards held by said tubular member and constituting a prismatic structure extending into the electron discharge space within said tube and a grid supported by and extending along said standards.

In testimony whereof, I have hereunto subscribed my name this 24th day of November, 1924.

DONALD G. LITTLE. 

